Brown marks on broad beans (the actual unripe seed).

Deleted by self.

 

Broad beans can actually get something called chocolate spot, but I've only ever noticed it on the leaves, but maybe it can get to the actual beans as well.

I seem to remember its caused or made worse by a shortage of potash.
But I think it might be fungal.

 

Cannot be much help here, but I have seen it on my autumn sown broad beans, but no idea what causes it.
Chocolate spot is mainly on the leaves, I lost a crop of dwarf broad beans to it.

 

After reading around two suggestions 1) Manganese deficiency, 2) Virus.